Characterization and Crystal Structure of Nickel Complexes of Imine Oximes Containing Tautomerized Enolate Ligands

The nickel (II) complexes 3-hydroxy-3-penten-2-one oximato-N,O(3-methylimino-2-pentanone oximato-N,N‘)nickel(II), Ni(pen)(mei); 3-hydroxy-3-penten-2-one oximato-N,O(3-ethylimino-2-pentanone oximato-N,N‘)nickel(II), Ni(pen)(eti); 4-hydroxy-4-hexen-3-one oximato-N,O(4-methylimino-3-hexanone oximato-N,N‘)nickel(II),
Ni(hex)(mei); and 4-hydroxy-4-hexen-3-one oximato-N,O(4-ethylimino-3-hexanone oximato-N,N‘)nickel(II), Ni(hex)(eti) have been synthesized from the corresponding alkyldione monoximes and amines and characterized by
NMR, IR, MS, and elemental analysis. The latter three complexes have not been previously reported, and the
characterization shows their structure to be contrary to that reported for Ni(pen)(mei) in earlier literature. Their
formation suggests two separate courses of the alkyldione monoxime:  reaction with amine to form the imine and
keto/enol tautomerization. The crystal structure of Ni(hex)(eti) has been determined:  monoclinic, P2(1)/n, a =
8.2350(1) Å, b = 14.0895(2) Å, c = 13.7965(1) Å, β = 95.964(1)°, with four molecules per unit cell. The
reactivity of the complexes is explained based on the crystal structure and 1H NMR data.